The present invention relates to a floppy or hard disc memory apparatus which serves for mass storage of information or data in a computation, word processing or other system.
Floppy discs are being widely used for mass storage in computation systems since they provide high access speed and high volume, consecutive storage. Typically, the disc is driven at constant speed and data written onto or read from a selected circumferential track in synchronism with constant frequency clock pulses. In a typical system, the disc has 77 tracks, each being capable of storing 26 sectors of data, each sector consisting of 128 bytes of data. Thus, each track stores 3328 bytes of data and the total capacity of the disc is 256,256 bytes.
The data density, or the number of bits per inch in the tracks, is maximized in the innermost track, and typically has a value on the order of 3268 bpi. However, due to the fact that the circumference of the outermost track is larger than that of the innermost track, the data density is only on the order of 1775 bpi in the outermost track. The difference is 1493 bpi, and constitutes wasted storage capacity since 1.84 times more data could be stored in the outermost track if the data density was the same as in the innermost track. The wasted storage capacity is also present in the intermediate tracks in a proportional manner. The outermost track is capable of storing 49, rather than 26, sectors of data at a density approximately equal to that of the innermost track, or 6272 bytes rather than 3268.